This study plans to learn more about how sleep loss impacts the way the body responds to sugar. This work will have important implications for development of treatments and countermeasures for people who are not able to get enough sleep for various reasons.

Participants will stay in the hospital for 6 days and will not be able to leave. Sleep habits will be measured for 7 days before the study. A research diet that is designed to maintain weight will be provided for 3 days before the study and during the study. Multiple tests will be performed, including metabolic testing and muscle and fat biopsies, both when participants first arrive and have had normal sleep and again after 4 nights of only 5 hours time in bed. The visit takes place at the Clinical Translational Research Center (CTRC) at the University of Colorado Denver, Anschutz Medical campus. It will take approximately 2 weeks to complete this study.

Inclusion criteria:

1. Healthy, lean participants.
2. No regular physical activity (<20 minutes/day). No exercise will be allowed for 3 days prior to study start.
3. Habitual sleep duration between 7-9.25h. Subjects must also be willing and able to keep a 9h time-in-bed schedule for 1 week prior to study admission.
4. Potential subjects must have lived at Denver altitude or higher for at least 3 months to inpatient study.

Exclusion Criteria:

1. Current or history of any clinically significant medical, psychiatric, or sleep disorder.
2. Use or history of any drugs, medications, supplements, caffeine, and alcohol.
3. Current or history of shiftwork in six months prior to laboratory study.
4. Travel more than one time zone in three weeks prior to laboratory study.
5. Blood donation in the 30 days prior to inpatient study.